N-carbobenzyloxy-L-glutamic acid-.alpha.-cholinester chloride has been in public knowledge to be useful as hypotensive drug, lipotropic drug and infantile paralysis therapeutical agent ("Jap. Chem. Soc., 72, No. 3. 46-47 (1951); Vitamin; 7, No. 4 (Separate Volume, 428-467 (1954)). According to said technical magazines N-carbobenzyloxy-L-glutamic acid-.alpha.-cholinester halide, which may be called a sort of the salt in the broad meaning, is inevitably obtained in the form of mixture with .gamma.-form in the known method. It is very difficult, however, to isolate N-carbobenzyloxy-L-glutamic acid-.alpha.-cholinester salt from the mixture to be purified, since said .alpha.- and .gamma.-forms are of extremely similar physicochemical properties due to their similar chemical structures as shown below;
N-Carbobenzyloxy-L-Glutamic Acid-.alpha.-Cholinester Salt (.alpha.-form) ##STR1##
Said X means a halogen or an organic sulfonate.